The present disclosure relates to battery packs. More particularly, the present disclosure relates to a battery pack in which a battery element is covered with an outer package.
In recent years, battery packs have been used as power sources for mobile electronic devices. In such battery packs, an outer package houses a protection circuit board, on which a protection circuit, etc. are mounted, and a battery element. As an outer package used for such a battery pack, a box-shaped package including upper and lower cases, etc. is widely used. For example, refer to Japanese Unexamined Patent Application Publication No. 2002-260608.
However, in the battery pack described above, when electrostatic discharge (ESD) occurs, static electricity may flow in the circuit board inside the battery pack, resulting in a malfunction of electronic circuits or damage to semiconductor elements. In order to solve such a problem, a technique has been proposed in which a conductive layer is disposed on the surface of a plastic molded case, and the conductive layer is connected to a negative electrode terminal of a battery. For example, refer to Japanese Unexamined Patent Application Publication No. 2007-323909. However, such a battery pack necessitates a great change in the design of the outer package of the battery pack.
Furthermore, when the battery pack described above is contained and used in an electronic device, such as a mobile phone, functional failure may be caused in the body of the electronic device due to the occurrence of ESD. In particular, in the case where the body of the electronic device has a structure having low tolerance to electrostatic discharge, the probability of occurrence of functional failure is high.
FIG. 26A is a schematic view showing a battery pack housing part of an electronic device, such as a mobile phone. As shown in FIG. 26A, in general, a battery pack housing part 101 is provided with openings 102, and a circuit board of the electronic device is exposed through the openings 102. In the electronic device having such a structure, when ESD occurs, there is a possibility that a conductive layer disposed on the surface of the outer package may form a static electricity path, and static electricity may flow in the circuit board exposed through the openings 102, resulting in a malfunction of electronic circuits or damage to semiconductor elements.
In order to solve the problem described above, it is conceivable to fill all the openings 102 of the battery pack housing part 101 with a plastic resin so that the circuit board of the electronic device is not exposed at the battery pack housing part 101, as shown in FIG. 26B. However, if such a concept is introduced, the design of the battery pack housing part 101 of the electronic device body is restricted. Under these circumstances, a technique has been proposed in which a component for protecting against electrostatic discharge (ESD) is added to a circuit of a battery pack.
FIG. 27A shows a circuit before addition of a component for protection against ESD. FIG. 27B shows a circuit after addition of a component for protecting against ESD. As shown FIG. 27B, a capacitor is provided between an identification terminal 111, which is referred to as a BSI terminal or an ID terminal, and a negative electrode terminal 112. However, even when such a component for protecting against ESD is added, it is difficult to obtain a sufficient effect. Furthermore, depending on the magnitude of electrostatic discharge, the added circuit may still be damaged, resulting in malfunction.
It is desirable to provide a battery pack in which ESD tolerance can be improved without greatly changing the design of the battery pack or a battery housing part of an electronic device body.